This invention relates to a mask blank glass substrate manufacturing method, a mask blank manufacturing method, a mask manufacturing method, a mask blank glass substrate, a mask blank, and a mask.
Conventionally, a mask blank, in which an optically readable area code is provided in the form of a metal film formed on an end surface or a back surface of a glass substrate, is known. (see, e.g. Japanese Unexamined Patent Application Publication (JP-A) No. 2002-116533). Further, a mask blank, in which predetermined symbols are marked on a side surface (end surface) of a glass substrate at its frosted portion, is also known (see, e.g. Japanese Unexamined Patent Application Publication (JP-A) No. S59-15938).
In recent years, the wavelength of an exposure light source has been reduced to 200 nm or less. Therefore, the quality (e.g. the allowable size of a defect, the allowable number of defects, or the in-plane thickness uniformity of a resist film that affects pattern characteristics of a device) required for a mask blank glass substrate or a mask blank has been becoming higher and higher. Depending on the manner of formation of an area code or the like, dust may be generated in a later process. Thus, it possibly becomes difficult to satisfy the required quality. Further, depending on the manner of formation of an area code or the like and the position of the formation thereof, the in-plane thickness uniformity of a resist film formed by the spin coating method may be degraded. Thus, it possibly becomes difficult to satisfy the required quality. Particularly, in the case of a thin resist film having a thickness of 300 nm or less for miniaturization of a pattern in recent years, the influence exerted on the pattern formation due to variation of in-plane thickness increases more than ever before and, therefore, the problem becomes more conspicuous. Further, also end surfaces are often mirror-polished in a mask blank glass substrate in recent years. Therefore, it is often difficult to obtain sufficient reading accuracy from clustered symbols or the like.